High Resolution Particle Sizing at Smaller Dimensions with Highly Focused Beams and other Non-Uniform Illumination Fields

ABSTRACT

A particle sizing method which allows for counting and sizing of particles within a colloidal suspension flowing through a single-particle optical sizing sensor SPOS apparatus using pulse height detection and utilizing non-parallel and non-uniform illumination within the sensing region of the flow cell. The method involves utilizing a deconvolution process which requires the SPOS apparatus to be characterized during a calibration phase. Once the SPOS apparatus has been characterized, the process of deconvolution after a data collection run, recursively eliminates the expected statistical contribution to the pulse height distribution PHD histogram in all the lower channels from the highest channel height detected, and repeating this for all remaining channels in the PHD, removing the contributions from largest to smallest sizes.

CROSS-REFERENCE TO RELATED APPLICATIONS

N/A

FIELD OF THE INVENTION

This invention relates to methods and apparatus for optical sensing,including counting and sizing of individual particles of varying size ina fluid suspension, and more particularly, to such methods and apparatuswhich yield higher sensitivity and detection at higher concentrationthan can be realized by optical sensors of conventional design.

BACKGROUND

In the world of SPOS (single particle optical sizing) and counting,traditional prior art has utilized a light field, as uniform inintensity throughout an illumination zone as possible, and in as tightlya structure as possible (small slice of light equals higher measurementconcentration limits), using various optical elements, and intersectthis illumination zone thusly created with particles suspended in afluid within a flow channel —sually encapsulated in a transparent flowcell. Laser light illumination is often preferred as it can be easilycollimated, and the monochromatic nature makes it easier to focus tosmaller regions.

Having a uniform light field interacting with a moving particle, makesthe first order correlation between particle size and pulse height adirect one-to-one relationship. The correlation between particlediameter and amount of light scattered and/or extinguished at microndimensions is to a first approximation linear (when viewed in log-logspace), and typically some of the non-linearities are removed by the useof a calibration curve. The calibration curve being a sort of a reverselook up table of pulse height to diameter.

Pulse height derived from the amount of light that was extinguished fromthe illumination source (extinction) as is measured at a detector, orthe amount of light that was scattered away from the beam in the forwarddirection (however detected) could be mapped to a diameter—often thoughtof as the diameter belonging to an equivalent cross-sectional area of asphere—as the absolute shape of the particle could not be determined bythis method. Calibration of the size (diameter) detected andverification of the method is accomplished with the use of preciselysized polystyrene (or other composition) spheres—commerciallyavailable—and size verified by microscopy techniques.

The industry understands the weakness of this method, only givingequivalent diameters, and uses other imaging techniques to gather themissing information, if needed. However, the ability to analyze areasonable volume of sample in about one minute of analysis time andcollect sufficient statistics as to be certain of the character of thesample, makes this a powerful technique, and is used in many fields.

Nature makes it difficult to squeeze light into a small space, and makeit uniform across a long enough region to usefully interact withpractical samples. Thereby limiting the smallest possible size one couldindividually detect and still have that one to one relationship withsize.

Advancements in the field of particle size detection (U.S. Pat. No.6,794,671 for Sensor-Design; U.S. Pat. No. 7,127,356 for an Algorithm;U.S. Pat. No. 7,496,463 for Baseline-Auto-Adjust), include the use of aparallel laser beam of small diameter to illuminate a tinier region thanthe usual slice of light traditionally used in SPOS (limited by thebehavior of light and the optics used) and to algorithmicallyreconstruct the particle size distribution after the pulse heightstatistics collection, since this method breaks the linear relationshipof pulse height to particle size. A smaller column of light allows oneto detect smaller diameter particles because the fraction of lightremoved from the probe beam (in relation to the total intensity of theprobe beam) is kept to a higher ratio, and their signal stays above thedetection limit. In other words, by keeping the ratio of the particlecross-sectional area to the cross-sectional area of the probe beam ashigh as possible pulses are created above the detection limit for muchsmaller particles than is possible by intersecting such particles withthe traditional slice of light as used in SPOS techniques who'scross-sectional area at the interaction zone is much larger than a roundand collimated pencil like beam.

This technique and algorithm require Gaussian illumination of the probebeam traveling in a parallel direction perpendicular to flow asparticles traverse the sensing zone of a flow cell.

However, both the type of illumination required and the need forparallel transversal through the flow cell create limitations to thistechnique and algorithm. The math used in the algorithm only works forGaussian illumination (a type of illumination that lasers in TEM00 modeexhibit, where TEM=Transverse Electromagnetic Mode.)

The limitation of the prior technique is that the detection of smallerdiameters comes at the cost of losing the one-to-one relationship ofeach particle's detected pulse height to its diameter, and having to usea parallel beam through the flow cell, limits the smallest diameter beamthat can be used within practical dimensioned flow cells. Additionallythe algorithm uses the tallest channel in the Pulse Height Distribution(PHD) of a mono-sized population to position the PHD vector in itsdeconvolution matrix, ignoring the populated, but smaller in heightchannels, formed by taller pulses.

Another limitation of the prior art technique is that for any givenincoming beam diameter as you attempt to focus a laser to an evensmaller spot with a focusing lens, the depth of focus also shrinks thesmaller in focus spot size you try to go. When the depth of focusbecomes smaller than the flow cell width that is traversed by the beam,the algorithm used to convert single pulse height to an individualparticle diameter fails and it no longer provides a way to correctlycorrelate pulse height to diameter.

Thusly, there is a need for a particle sizing method that is viable forand sensitive to smaller diameters, using light that is focused astightly as possible only limited by nature. This is achieved by usingnon-parallel and non-uniform illumination in the direction of the lighttravel within the sensing region of the flow cell. The techniquedescribed in this patent allows for the use of light focused as tightlyas possible (diffraction limit) for any given hardware, and it alsoallows for the use of multiple light sources and complicatedillumination fields—including folded and reflected light—or anyirregularities in the probe beam such as results from imperfect opticalelements and imperfect probe beams.

SUMMARY

It is the object of this invention to provide a high resolution and highconcentration particle sizing methods than is currently not possibleusing previous techniques.

The particle sizing method of the current invention allows for actualsizing of particles using pulse height detection from a sensor byutilizing non-parallel and non-uniform illumination within the sensingregion of the flow cell. The ability to measure particles at thesub-micron dimensions one at a time is achieved by focusing the laserbeam to the point where the beam is no longer uniform and parallel inthe direction of the light travel within the flow cell.

In order for the method of the current application to utilize a beamdiameter and focus elements where the depth of focus is smaller than theflow cell width, a new, novel, method of deconvolution was developed.

The deconvolution process requires the sensor to be characterized usingmultiple histograms that are collected during the calibration phase ofthe sensor. Once the sensor has been characterized, the process ofdeconvolution after a data collection run, recursively eliminates theexpected statistical contribution to the histogram in all the lowerchannels from the highest particle height detected and repeating thisfor all remaining channels in the pulse height histogram, removing thecontributions from largest to smallest channels. The logic followed isthat pulses in the histogram channel representing the strongest detectedsignal, could have ‘ONLY’ come from the brightest part of theillumination zone for any given particle diameter. The remaining lowerintensity channels (in the same histogram) are populated with pulsesoriginating within the detection zone, but away from the brightest spot.The whole histogram being one of the characterizing histograms for aparticular diameter probe-particle collected during the calibrationprocess of the sensor. Since ‘Brightest Spot’ is not limited to beinggenerated by a uniform and circular beam—this technique works for allsorts of shapes in the illumination field—since there will be ‘A BrightSpot’ somewhere within the illumination field, and all other positionswill by definition have a lower intensity (and resulting is less tallpulses at the detector). It is noted that this method results inhistograms where the channel with the most counts need not be thechannel with the tallest pulses and often is not. The channel with themost counts in the histogram is often produced by other (less intense)illumination regions within the sensing zone where a larger fraction ofthe probe-particles traverse.

Once the deconvolution process is complete, the resulting output is aparticle size distribution (PSD). Peaks in the particle sizedistribution are located at channel numbers that are not yetrepresentative of a size. Transformation of the channel number to aspecific particle size is achieved using a calibration curve—whosemapping of channel number to diameter has been previously determinedduring the calibration phase of the sensor. The particle sizing methodof the current invention allows for single particle size detection andmeasurement below 100 nanometers within practical flow cells.

Since particles are detected from such small volumes in relation to thevolume of the flow cell in the region of the sensing zone, an additionalcorrection needs to be applied in order to recover the concentration(particles per unit volume) of the colloidal suspension. During thecalibration phase of the sensor—a table is constructed that records thefraction of particles detected at a particular diameter, and thisinformation is used to calculate the concentration of the suspensionafter a data collection run. This is the detector efficiency at a givensize (see detector efficiency FIG. 3).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic of the prior art optical scheme typicallyused in the preferred embodiment of the current invention andconventional prior art light extinction sensor;

FIG. 2 is a diagram depicting the behavior of light passing through afocusing lens and through the region of focus;

FIG. 3 is a graph depicting the detection efficiency for variousparticle sizes in a colloidal suspension for a given sensorconfiguration;

FIG. 4 is a graph depicting the signal intensity at various scatterangles for a given particle size;

FIG. 5 is a chart of signal intensity vs. time and the resulting pulsesfrom a scatter detector as a colloidal suspension travels through theflow cell;

FIG. 6 is a chart of signal intensity vs. time and the resulting pulsesfrom an extinction detector as a colloidal suspension travels throughthe flow cell;

FIG. 7 depicts various beam profiles as each beam propagates through aflow cell, while holding illumination wavelength and focal length offocusing lens constant;

FIG. 8 depicts the effects on the Pulse Height Distribution collected,for various Beam Diameters, while holding particle diameter,illumination wavelength, and focal length of focusing lens constant;

FIG. 9 depicts the various Pulse Height Distributions generated byvarious particle sizes, while holding beam diameter, focusing lens focallength, wavelength of illumination source and flow cell dimensionsconstant;

FIG. 10 depicts a Pulse Height Distribution (PHD) histogram of the pulseheights seen during a data collection session, tabulated according totheir height, measured in volts, displayed in the graph above as Countsvs. Pulse Height;

FIG. 11 is a three-dimensional depiction the illumination zone and thesensing zone inside a flow channel;

FIG. 12 is a cross-section of the illumination zone and the sensing zoneinside a flow channel;

FIG. 13 is a three-dimensional close-Up view of the sensing zone for oneparticular configuration of beam diameter, wavelength of light andfocusing lens focal length;

FIG. 14 is a graphical representation of a pulse height distributioncalibration curve representing the signature resulting from a mono-sizedparticle population, and a particular sensor configuration;

FIG. 15 is a flow chart of the deconvolution algorithm to convert apulse height distribution to a particle size distribution;

FIG. 16 is a graphical representation of a pulse height distribution(PHD) calibration curve, and the resulting particle size distribution(PSD) for one mono-sized population, with four of the sensor calibrationcurves also represented;

FIG. 17 is a graphical representation of a pulse height distribution(PHD), and the resulting particle size distribution (PSD) for threemono-sized populations in colloidal suspension;

FIG. 18 is a graphical representation of experimental data collected for0.993 μm diameter latex micro-spheres in comparison to a simulation ofthe same experimental conditions;

FIG. 19 illustrates a schematic of an optical scheme typically used inthe first alternate embodiment of the current invention;

FIG. 20 illustrates a schematic of an optical scheme typically used inthe second alternate embodiment of the current invention;

FIG. 21 illustrates a schematic of an optical scheme typically used inthe third alternate embodiment of the current invention;

FIG. 22 illustrates a schematic of an optical scheme typically used inthe fourth alternate embodiment of the current invention;

FIG. 23 illustrates a schematic of an optical scheme typically used inthe fifth alternate embodiment of the current invention;

FIG. 24 illustrates a schematic of an optical scheme typically used inthe sixth alternate embodiment of the current invention;

FIG. 25 illustrates a schematic of an optical scheme typically used inthe seventh alternate embodiment of the current invention;

FIG. 26 illustrates a schematic of an optical scheme typically used inthe eighth alternate embodiment of the current invention;

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENT

Referring to FIG. 1, the equipment arrangement for the preferredembodiment to perform the particle sizing method of the currentinvention comprises a flow channel 1 through which a colloidalsuspension 2 is traversing, an illumination source 3, a focusing lens 4,a detector 5, and a current to voltage converter (not depicted), a meansof causing the colloidal suspension to traverse the flow cell such as apump (not depicted), and associated collection electronics (notdepicted).

The flow channel 1 of the preferred embodiment allows light from theillumination source 3 to pass through a focusing element 4, enter theflow channel 1, come to a focus in the center of the colloidalsuspension 2 and exit the other side of the flow channel 1 to thedetector 5 utilizing transparent walls though which the laser beam 7 cantransverse. Flow channels 1 for fluid samples are typically made ofquartz glass, but any transparent material that forms a flow channel 1works. The material composition of the flow channel 1 is usually chosento be compatible, and not chemically interacting with, the colloidalsuspension 2.

As known to those practiced in the art, the internal dimensions of theflow channel 1 are chosen in such a way as to maximize certain datacollection parameters, as benefits the measurement. For instance,squeezing flow through a narrow flow channel 1, helps with highconcentration colloidal suspensions 2, making it easier to get aparticle 6 alone in the sensing zone 8, and thus tabulated by theelectronics, at the cost of higher particle velocity (shortermeasurement time), and the possible clogging of the flow channel 1 dueto the narrowness of the flow channel 1. Whereas a wide channel 1 helpswith not clogging the flow channel 1 and easier cleaning, at the cost oflower concentration in the measurement. When the transporting fluid isair or an inert gas, the flow channel 1 can include simple windows inorder to protect the optics from contamination and enable easiercleaning. In-between measuring one sample and the next one the userusually flushes the flow channel 1 out with particle free compatibleliquid. This is done in order to minimize contamination from one sampleto the next.

For practicality, flow channels 1 have to be large enough so as to notclog when exposed to a colloidal suspension 2. There are times the flowchannels 1 must be cleaned by either, or both mechanical means andchemical means as some samples can be nasty and harsh on cells. There isa practical lower ‘width’ one can make a flow channel 1 so as to avoidclogging by the colloidal suspension 2, and that a pump can push thecolloidal suspension 2 through, and enough volume of the colloidalsuspension 2 can be processed in reasonable time in order to collectuseful statistics.

The colloidal fluid suspension 2 is comprised of a mixture in which onesubstance of dispersed insoluble particles 5 is suspended throughout atransport fluid substance, but not chemically interacting with it.Typically the particles 6 are comprised of various sizes. The transportfluid substance is sufficiently transparent or translucent to allowlight to travel through the colloidal fluid suspension 2 as it travelsthrough the flow channel 1.

The illumination source 3 of the preferred embodiment is a laser beam 7.Since monochromatic light can be focused to a smaller spot, and lasersare the illumination of choice for monochromatic light, this inventionis best advantaged using a laser beam 7. However, this can be achievedthrough multiple embodiments known to those skilled in the art.Alternatively the illumination source 3 can introduce light into theapparatus through an optical fiber, or two fibers can be positionedfacing each other at close proximity inside the fluid flow, requiring nofocusing lenses, where one fiber brings light into the illumination zone10, and the other fiber removes light from the sensing zone. Even thoughno focusing need be present with fibers, the sensing zone 8 is a volumemade from the intersection of the illumination zone 10 and the volumewhere sufficient signal strength is generated and is detected.

The mathematics of recovering the Particle Size Distribution (PSD) fromthe Pulse Height Distribution (PHD) as introduced in this patent,applies to all manner of illumination 3, not just monochromatic light.The PHD for poly-chromatic light will be different from mono-chromaticlight for a given particle diameter, beam 7 diameter, focusing lens 4and flow channel 1, however the PSD will be the same.

The focusing lens 4 of the preferred embodiment focuses the light source3 to a spot, typically utilizing a focusing lens 4 composed of a singleoptical element or multiple optical elements. To help with the detectionof smaller particles 6, a smaller spot focus inside the detection zonecan be achieved by using a wider source laser beam 3 and/or a shorterfocal length lens 4. The relationship between wavelength of light, focallength of lens, and width of incoming illumination beam having the formof EQN 1 is depicted in FIG. 2, where W₀ is the width at best focus, Ais the wavelength of light, f is the focal length of the focusing lens4, and W_(D) is the width of the incoming beam 7. The depth of focus,having the form of EQN 2, as measured from the points where the beamwidth is √2·W₀ on either side of the best focus point. FIG. 7 depictsthe profiles for various diameter beams 7 as the light travels throughthe flow cell 1. At small spot sizes, the depth of focus is too shortand is completely inside any usable flow channel 1, therefore itrequired a new approach to deconvoluting the pulse height distributioninto a size distribution. The previous technique breaks down, and you nolonger get a usable answer.

$\begin{matrix}{w_{D} = \frac{\lambda f}{\pi w_{0}}} & {{EQN}\mspace{14mu} 1} \\{{2{Zr}} = \frac{8\lambda\; f^{2}}{\pi\; w_{D}^{2}}} & {{EQN}\mspace{14mu} 2}\end{matrix}$

The detectors 5, 106 of the preferred embodiment are typicallyphoto-diodes. The detectors 5, 106 are fast enough in response andusually cover the range of light frequencies of the illumination source3. They are used in a scattering or extinction configuration, and oftensimultaneously applied to the same sensing event. Extinction is when allthe light from the illumination source 3 is captured at the detector 5,and the detection event is the measure of the amount of light removedfrom the light path because of a particle 6 passing through the sensingzone 8. Scattering detectors capture photons that are diverted fromtheir forward path, due to interaction with the particles 6 in thesensing zone 8 and are diverted to any series of angles away from theforward direction they were traveling. Scattering detectors can be inmany configurations and capture various scattering angles both in theforward or backward scattering direction. Any other extinction detector5 and/or scattering detector 106 capable of capturing and measuring theintensity of scattered light or the reduction in beam intensity andresponding fast enough to a sensing event in the flow channel 1, canserve the purpose of providing signal to the collection electronics.

The colloidal suspensions 2 to be measured can be transported throughthe flow channel 1 utilizing pumps to generate the motive force. Anymeans of transporting a colloidal fluid 2 suspension through said flowchannel 1 can be used. Those skilled in the art can use a pump, gravity,pressure, vacuum, or other means of transporting the colloidalsuspension though the flow cell. A pump is often preferred because apump can have predictable flow rates which help in the sampleconcentration calculation. The fluid suspension is transported throughthe flow channel 1 at velocities that the interaction with the probebeam generates signal that is within the design parameters of thedetector 5.

The sensing zone 8 is the portion of the illumination zone 10 inside theflow cell that generates signal seen at the detectors. When the numberof particles detected at the sensing zone are ratioed with theconcentration of the sample, this determines the visibility fraction ofthe sensor for a given particle size, and if this computation is donefor each size in the PHD histogram an efficiency curve is generated forthe sensor. This is done during the calibration phase of the sensor andused in the data collection phase to report the concentration of thesample just measured. A typical sensing zone 8 is created by introducinga focusing lens 4 in the path of a collimated laser beam 7 and locatingthe point of best focus inside the flow channel 1 of a transparent flowcell and having detectors 5 of sufficient sensitivity to record theinteractions of the light with the flowing particles. FIGS. 11, 12 and13 depict the illumination zone 10 and the sensing zone 8 inside a flowchannel 1.

Knowing the visibility fraction for a detector 5 and for a givendiameter, one can calculate the concentration of the measured colloidalsuspension 2 at this diameter. One would do this calculation for allparticle 6 diameters measured to derive the concentration of the sourcefluid. FIG. 3 depicts a typical graph depicting the detection efficiencyfor various particle sizes in a colloidal suspension 2 for a givensensor configuration.

The signal that is sensed at the detector 5 is generated by theinteraction of the light that arrives into the illumination zone 10 froman illumination source 3, interacting with a colloidal fluid suspension2 particle 6 passing though the illumination zone 10 at a particularpoint in time, as it is transported by a carrier fluid. The lightinteracts with a particle 6 and ‘scatters’ in all directions around theparticle 6. The detector 5 that is looking at the laser beam 7 head-on,the Extinction Detector, senses this as light removed, and it reportsthe intensity as dipping in value, whereas a detector 106 placedoff-axis to the laser beam 7 and shielded from the illumination comingfrom the beam, the Scatter Detector, whether in the forward direction(forward scatter 505), or in the reverse direction (back scatter 405),reports an increase in intensity. The intensity of the reported signal,in either case, contains information about the diameter of the particle6. FIG. 4 is a graph depicting the signal intensity at various scatterangles for a given particle size.

Signals from the extinction or scattering detectors 5 are oftenprocessed via an Analog to Digital Converter, converted to a digitalform and then stored and processed inside suitable computing hardware.The traversal of a particle 6 through the sensing zone 8 generates apulse that the collecting electronics, measures the pulse height andother parameters, and then tabulates the values in various histograms.The histogram of pulse heights is the pulse height distribution (PHD)that then gets processed further in the deconvolution algorithm torecover the particle size distribution (PSD). Besides digitalprocessing, pulse heights can also be discriminated by analog circuitmeans, but the histogramming of any resulting pulse heights requires theuse of digital hardware. FIG. 5 is a chart showing the voltage ofdetected pulses as a colloidal suspension travels through the flow cellusing a Scatter Detector 106. FIG. 6 is a chart showing the voltage ofdetected pulses as a colloidal suspension travels through the flow cellusing an Extinction Detector 5.

Referring to FIG. 9, to perform the particle sizing method of thecurrent invention a collection of curves that characterize a sensor isgenerated. All parameters are kept constant and particle size isstepped, so that response curves for each size is collected. Knowing thebehavior of such a sensor for all diameters in its detection range,provides data necessary to deconvolute a pulse height distributioncollected from an arbitrary colloidal suspension, into a sizedistribution.

For a given sensor configuration, multiple histograms are collectedduring the calibration phase of the sensor. Each histogram represents amono-sized colloidal population of known size. During the calibrationphase a sensor is characterized, and the data collected represents apulse height distribution calibration curve for this sensor.

Sensor characterization can be done experimentally or via computersimulation. If done experimentally with size-traceable mono-sizedparticle standards of known concentration, the experiment will alsosimultaneously derive an accurate calibration curve for the thuslyconstructed sensor, along with its associated efficiency data. Theprocess of characterization of a sensor also produces a usefulcalibration for the sensor where channel number in the histogram can becorrelated to size.

Referring to FIG. 14, for a pulse height distribution calibration curve,there is an upper most channel (right most channel in the graphreferenced above) where there are no counts beyond that channel. Thishappens because any given mono-sized population can only generate apulse of maximum size (volts) when the particles pass through the centerof the brightest spot in the illumination field. In this curve, theright most channel with counts greater than zero becomes the anchoringchannel that selects where this curve will be used in the deconvolutionprocess, in other words, the right most channel becomes the channel thatdefines the curve position, with the relative height of that channel (inrespect to total counts) containing useful information as to therelative contribution of every other channel in any unknown PHD. Eachchannel in the histogram has such a characterization curve assigned toit. For channels that have no curves measured or computed, the processof interpolation and extrapolation can be used to fill in from knownadjacent curves.

If the colloidal concentration (particles per unit volume) of theintroduced mono-sized sample is known at the time of characterization,then an efficiency factor for that mono-sized sample can be also becomputed and saved in the sensor characterization database, to be usedduring a future run to calculate the concentration for this diameter inthe sample under test. This is possible since knowing the concentrationof the mono-sized population during characterization, and the physicaldimensions of the flow channel, one can determine the ratio of what isvisible (counted) and what was computed to be present during the datacollection period. This step is optional and provides additionalconcentration information if it so desired.

Once a sensor configuration has been characterized and the pulse heightdistribution calibration curves have been generated (the sensor isdeemed to be calibrated), one would then run a colloidal suspension tobe analyzed through the equipment arrangement for the preferredembodiment, known as a data collection session. Referring to FIG. 10,the output from the equipment arrangement is a histogram of the pulseheights seen during a data collection session, tabulated according totheir height (measured in Volts), displayed in the graph as Counts vs.Pulse Height.

Referring to FIG. 9, the process of deconvolution is completed byrecursively eliminating the expected statistical contribution to the PHDhistogram in all the lower channels from the highest particle heightdetected, and repeating this for all remaining counts in the pulseheight histogram, removing the contributions from largest to smallestchannels. Referring to FIG. 15 the deconvolution process is completed byfirst examining every channel one at a time in the collected PHD,starting with the ‘right most’ channel (in other words, the histogramchannel that represents the tallest pulses tabulated). From this, thecalibration curve representing that channel is retrieved from memory,and the height of the collected PHD channel is multiplied with everyelement of the calibration curve for this channel, thus producing a newPHD histogram of the expected contribution to the collected PHD for thisdiameter particle. Note, the calibration curve has previously beennormalized to a value of one (1.0) at the channel that it represents(defining channel—ie. the upper most channel with counts in it)—with allother channels taking on relative counts in relation to the definingchannel (this is the NormToOne(Calvec[][]) step in FIG. 15).

Following this step it is known what the contribution in counts was intothe collected PHD from all the channels from a particle this size. Oncedetermined, subtract this computed PHD for this size from the collectedPHD, essentially eliminating from the collection the contribution ofparticles of this diameter. What is left behind after the subtraction isthe contribution to the PHD from particles of smaller diameters. Theheight of the current channel in the PSD is established from thequantity of counts that were in the collected PHD histogram for thischannel. This process is repeated for all channels going down to channelone, at the left side of the histogram (as seen in FIGS. 16 and 17),sequentially eliminating the contribution to the PHD from particles ofvarious diameters.

The reason that this computation is done starting at the channelrepresenting the tallest pulses and working toward the channelsrepresenting the smallest pulses, is that it can be definitivelydetermined that the counts in the upper most channel (where counts arepresent) were derived from interactions of the largest particles in thecolloidal suspension and the brightest portion of the illumination beam.What diameter particle created tallest pulse detected can be determinedbecause the sensor has previously been characterized. Thecharacterization spectrum of a sensor for any given mono-sizedpopulation is normalized to unity on the highest channel containingcounts, since that is the only channel that which is known how thecounts got there (from the brightest spot in sensing zone) during thedeconvolution process. For every channel smaller than this it cannot bedetermined if a pulse was generated by a particle passing through thebrightest portion of the illumination zone, or an even bigger particlepassing through a section of the illumination zone where the intensityis lower. This ‘pealing of the onion’ from a position in the PHD whereone can proportionally remove the counts introduced by the lowerchannels during the analysis to know exactly how the pulse height gotgenerated for that channel, and computationally going to a lower channelwhere it cannot be determined what size particle generated the capturedpulses that were tabulated into that channel—is the algorithmicdeconvolution of the PHD into a PSD.

Referring to FIGS. 16 and 17, once the deconvolution process iscomplete, the resulting output is a particle size distribution (PSD).Peaks in the Particle Size distribution are located at channel numbersthat are not yet representative of a size. Transformation of the channelnumber to particle size is achieved via an prior art industry standardcalibration curve where the voltage representing a particle diameter ofa particular size, is converted to a size by means of a look up table orfunction curve.

A limitation to the particle sizing method of the current invention isthat the technique breaks down when there is an insufficient number ofpulses detected to be able to deconvolute with confidence, especially iffaced with a poly-dispersed sample. This is a problem of statisticaluncertainty and confidence in the answer.

There is some art in deciding when enough pulses have been collected toaccurately represent a colloidal population. In a mono-sized colloidalsuspension a minimum of 10,000 events can accurately characterize thesize of the particles—while counting in the millions (total PHD counts)just reinforces the confidence for the size initially detected. Run timelimitations come into effect, where collecting data for a longer timedoes not produce any more information besides reinforcing the earlieranswer and only improving the concentration statistics. Inpoly-dispersed colloidal suspensions 100,000 counts are a low minimum inconstructing a spectrum and ideally counts in the millions in the PHDwill improve the quality of the answer. The quantity of counts detectedis a quality issue and it depends on the needs of the user as to howcertain they need to be of what is being tested. Sometimes samplevolumes are so small or samples are very dilute providing fewer countsthat one would feel comfortable sensing, but such are the trade-offs ofmeasurement.

The result of this limitation is that the sensors as described in thisapplication are not useful in contamination monitoring where few largeparticles in the population are in need of detection and correctlysized. However, the particle sizing method of the current invention canstill be used to bound the range of particle diameters observed, withoutproviding a detailed PSD. A sensor of this type can still provide usefulsample information if given enough data collection time when the sampleis highly dilute.

Referring to FIG. 19, a first alternate embodiment of the sensor iswhere light from an illumination source 103 is focused by means of alens 104, through a flow channel 101, having the focal point positionedinside the flow channel 101, as a colloidal suspension 102 is traversingsaid flow channel 101, and a signal is generated from particles 107flowing past the illuminated zone inside the flow channel 101 as theyinteract with the illumination zone. Two detectors 105, 106 are used,one 105 to capture signal that is extinguished from the illuminationsource 103, and a second detector 106 to capture signals that aregenerated by the light as it scatters off the traversing particles 107.Deconvolution from PHD to PSD is done via the same algorithm for bothchannels, adjusting for the fact that extinction pulses are negativegoing, whereas scattering pulses are positive going.

Referring to FIG. 20, a second alternate embodiment of the sensor iswhere light from an illumination source 203 is focused by means of alens 204, through a flow channel 201, having the focal point positionedinside the flow channel, as a colloidal suspension 202 is traversingsaid flow channel 201, and a signal is generated from particles flowingpast the illuminated region inside the flow channel 201 as they interactwith the illumination zone. One detector 205 is used that senses lightthat is back-scattered from the traversing particles 207 as theyinteract with the illumination zone. The forward beam is blocked anddiverted to an absorbing medium 206 as to not interfere with the signalat the back-scatter detector 205. Deconvolution from PHD to PSD is donevia the algorithm disclosed herein.

Referring to FIG. 21, in a third alternate embodiment the particlesizing method of the current invention is not limited to a single lightsource but works for a number of different light sources 303, lenses 304and detectors 305 in the probe light beam(s) through the flow channel301. These alternate embodiments are possible because having one or manybrightest spots generating signal from the particles 307 in thesuspension 302 is of no importance in the characterization of thesensor. The brightest spot or spots will produce the tallest pulses fora given size probe particle is what matters. The quantity of spots willchange the distribution of counts in the remaining spectrum, but that iswhat characterization is about, to record such behavior. One might usemultiple focused spots to generate signal from multiple locationsthereby increasing the efficiency factor of what is ‘seen,’ at the costof lowering the operating concentration of the sensor, as a practicaltrade-off. The observation above is powerful in that it opens the doorto alternate embodiments of sensors using the same characterizationapproach to achieve a size distribution from a pulse heightdistribution. Alternatively, in this configuration, the signal from eachdetector can be processed separately into separate PHDs, and by usingdifferent focal length lenses, 3 PHD's can be simultaneouslyconstructed, each covering pulses from a different size range. This ineffect expands the dynamic range of the sensor. Each ‘channel’ wouldhave to have its own characterization spectra to apply to the respectivePHD's.

Referring to FIG. 22 in a fourth alternate embodiment, whereby a sensorcan be constructed having focused light introduced into an opaque flowchannel 401 through a window 406 on the side of the flow channel 401 asa colloidal suspension 402 is flowing in the flow channel 401 inconjunction with a back scatter detector 405. Back Scatter occurs whenlight from the beam and particle 407 interaction, travels in thebackward direction relative to the beam direction. This light iscollected at a detector 405 and processed through the countingelectronics, where the detector 405 is located adjacent to the lightsource 403 and lens 404 and with a view of the region of focus, thedistribution of particle sizes is characterized by this means.

Referring to FIG. 23, in a fifth alternate embodiment the scatterdetector 505 can be behind a mask 506 that blocks light from theillumination source 503, through the lens 504 and flow channel 501 fromreaching the detector 505, but allows light scattered from a particle507 from the sensing zone to impinge on the detector 505. A mask 506 isan opaque surface that blocks light from passing through it. Often masks506 are strategically placed in order to block view of the illuminationsource 503 from the detector, or to select a subset of scattering anglesof a signal as it travels to the detector 505, limiting the detectionregion for a higher concentration. This approach works for wet (liquidcolloidal suspension) or dry (particles transported by a gas) particlesizing.

Referring to FIG. 24, in a sixth alternate embodiment a sensor can beconstructed having focused light from a light source 603 and lens 604introduced into a capillary flow channel 601 through the flow channel'stransparent walls, as a colloidal suspension 602 is flowing in thecapillary 601. The light is collected at the extinction detector 605 andprocessed through the counting electronics. The distribution of particlesizes 607 is characterized by this means. Any distortion in the beamcaused by the imperfect manufacture and small diameter of the capillary601 creates an imperfect focus spot, but the nature of this inventioncan deal with imperfect illumination zones, and properly deconvolute theresulting PHD's into PSD's.

Referring to FIG. 25, in a seventh alternate embodiment of this method,is a sensor comprising of a light source 703, lens 704, and fiber 705introducing light into a sensing zone in the flow channel 701, spreadingout in a cone of light, and another fiber 706 and detector 707 closelyspaced opposite and co-linear, detecting pulses from its own cone ofacceptance. This technique is used to derive a size distribution of whatparticles 708 pass between the fibers 705, 706. The fibers 705, 706 canbe slightly retractable, with the resulting sensor now made easier toclean, and freed from any jamming debris. Due to the largerlight/particle interaction volume (sensing zone), which is not a focusedspot, makes this arrangement best suited for use with lowerconcentration colloidal suspensions 702.

Referring to FIG. 26, in an eighth alternate embodiment of this method,the sensor is comprised of two parallel fibers 805, 806 in a probeconfiguration, one supplying light 805 from a light source 803 and lens804 and the other detecting the back-scatter 806. The probe introducedinto a moving colloidal suspension 802 of sufficient dilution flowingthrough the flow channel 801 that individual pulses from particles 808can be sensed by the back-scatter detector 807, and their sizedistribution thusly characterized. The spreading nature of the lightmakes this is a low concentration sensor.

The corresponding structures, materials, acts, and equivalents of anymeans or step plus function elements in the claims below are intended toinclude any disclosed structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of the present disclosure has been presentedfor purposes of illustration and description, but is not intended to beexhaustive or limited to the disclosure in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of thedisclosure. The aspects of the disclosure herein were chosen anddescribed in order to best explain the principles of the disclosure andthe practical application, and to enable others of ordinary skill in theart to understand the disclosure with various modifications as aresuited to the particular use contemplated.

What is claimed is:
 1. A method for creating a particle sizedistribution PSD of particles in a fluid suspension of unknowncomposition comprising: providing a single-particle optical sizingsensor apparatus wherein a beam of light is directed through ameasurement flow channel to form a non-uniform sensing zone within themeasurement flow channel; wherein in the non-uniform sensing zone thebeam of light comprises an illumination field with a smallest focusregion where maximum illumination intensity is reached and a largestfocus region where minimum illumination intensity is reached; whereinthe single-particle optical sizing sensor apparatus further comprises adetector which detects when particles traverse the non-uniform sensingzone and interact with the illumination field, and outputs signals ofvarying pulse heights, depending on the particle size and location ofthe particle within the non-uniform sensing zone; wherein the signals ofvarying pulse heights are organized into a pulse height distribution PHDwhere a largest particle passing through the smallest focus region ofthe non-uniform sensing zone will create a tallest pulse height and asmaller particle will create a smaller pulse height; creating aplurality of normalized characterization PHDs; creating a data set PHDof the fluid suspension of unknown composition by flowing the fluidsuspension of unknown composition through the single-particle opticalsizing sensor apparatus and recording the output signals of thedetector; deconvoluting the data set PHD by removing contribution of thelargest particle travelling through the smallest focus region of thenon-uniform sensing zone from the data set PHD by locating the tallestpulse height within the data set PHD, locating the characterization PHDwhich has a correlating tallest pulse height, multiplying the pulseheight of the largest particle with the normalized correlatingcharacterization PHD to create a contribution PHD, and subtracting thecontribution PHD from the data set PHD; iteratively deconvoluting thedata set PHD by removing contribution of each subsequent channel in thedata set PHD by similarly looking up correlating characterizing PHDs,multiplying the pulse height of the largest particle with the normalizedcorrelating characterization PHD to create a contribution PHD, andsubtracting the contribution PHD from the data set PHD, eventuallyresulting in a PSD.
 2. The method of claim 1, where the method ofcreating the characterization PHDs comprises flowing a plurality offluid suspensions of known composition through the single-particleoptical sizing sensor apparatus, recording the output signals of thedetector, and normalizing the output signals of the tallest pulse heightin the characterizing PHD to a value of one.
 3. The method of claim 1,where the method of creating a data set PHD further comprisesrecursively eliminating the expected statistical contribution to thedata set PHD after recording the outputs signals of the detector.
 4. Amethod for deconvoluting a pulse height distribution PHD of a fluidsuspension of unknown composition flowing through a single-particleoptical sizing sensor apparatus that utilizes a non-parallel andnon-uniform beam profile, said method comprising: creating a pluralityof normalized characterization PHDs; identifying a tallest pulse heightin the PHD of a fluid suspension of unknown composition and identifyinga correlating characterization PHD with a same tallest pulse height;creating a contribution PHD by multiplying one channel of the PHD of afluid suspension of unknown composition and the correlating normalizedcharacterization PHD; subtracting the contribution PHD from the PHD of afluid suspension of unknown composition to create an intermediate PHD;repeating this process for the next remaining tallest pulse height inthe intermediate PHD until the PHD of a fluid suspension of unknowncomposition has been completely deconvoluted into a PSD.
 5. The methodof claim 4, where the method of creating the characterization PHDscomprises flowing a plurality of fluid suspensions of known compositionthrough the single-particle optical sizing sensor apparatus, recordingthe output signals of the detector, and normalizing the output signalsof the tallest pulse height in the characterizing PHD to a value of one.6. The method of claim 4, where the method of creating a data set PHDfurther comprises recursively eliminating the expected statisticalcontribution to the data set PHD after recording the outputs signals ofthe detector.
 7. The method of claim 4, where the single-particleoptical sizing sensor apparatus utilizes extinction detection.
 8. Themethod of claim 4, where the single-particle optical sizing sensorapparatus utilizes scatter detection.
 9. The method of claim 4, wherethe single-particle optical sizing sensor apparatus utilizes bothextinction detection and scatter detection.